The aerodynamic efficiency of wind turbine blades is a key factor that determines how efficiently a wind turbine generator is able to extract energy from a flow of wind. To this end, modern utility scale wind turbines usually have blades whose precise aerodynamic profile is crafted so as to maximise lift along the entire blade length so as to optimise efficiency.
The surface characteristic of a blade is also important in that it should be smooth and uniform so as to maintain laminar airflow across the aerofoil section of the blade to promote good lift characteristics. However, as the wind turbine blade rotates, it will tend to accumulate a layer of dirt which has the effect of reducing the aerodynamic efficiency of the blade. It is therefore desirable that the blades of a wind turbine are cleaned periodically to remove the accumulation of dirt, thereby helping to keep that blade at its peak aerodynamic efficiency.
One approach is described in EP1583905B1 in which an aerial work platform is arranged to encircle the blade and to move vertically with respect to the blade whilst applying a surface treatment to it. In one example, the platform is mounted to the end of an extendable lifting arm that provides positional control over the platform so that it can be moved vertically with respect to the blade under the control of a suitably trained operator. In another example, the platform is coupled to a cable hoist arrangement. In this arrangement, the platform is suspended from a series of cables that depend downwardly from a root end of the blade where they are connected to a frame. Bottom ends of the cables are connected to a stable base, in this case provided by a vehicle. The platform is configured to move up and down along the cables, which act as a guide for the work platform to ensure that it moves along a substantially linear vertical path. Both schemes are complex and likely to be time consuming which extends the total time and also the cost of that maintenance task. In addition, the ring-like structure of the platform results in a cascade of fluid from the platform to the surface below it, and much of this fluid can be considered wasted.
It is against this background that the invention has been devised.